Because of the potential danger presented by being exposed to continuous, albeit small microwave fields generated by microwave energy passing through deteriorated microwave oven doors, police radar speed monitors, telephone and television relay stations, diathermy machines, wood or rubber curing plants emitting microwave fields, it is imperative that this energy be monitored. To effectuate this purpose, a simple and efficient monitoring expedient should be conveniently available at the site of use. This is particularly important with respect to microwave ovens, since the seals and shoulders used to prevent the microwave energy from escaping into the household environment progressively deteriorates such that a once-safe oven gradually emits more and more energy into the environment to the detriment of the people in the vicinity of such an oven. Therefore, a detector is needed which enables a user to quickly and easily determine the presence of such a leak in the home, factory or commercial establishments before any harm occurs.
Various microwave power detectors have been developed for this purpose. One such detector has been described in U.S. Pat. No. 4,032,910 issued to Hollway et al. This patent discusses a detector which includes a dipole antenna, a hot carrier diode and a light emitting diode used to indicate whether the detector senses a microwave field greater than a predetermined value. As shown in FIG. 3 of Hollway et al, an antenna is placed across a hot carrier diode. A silicon controlled rectifier is connected in series with an audio or visual alarm such as an LED which is triggered by a signal level derived from a potential divider connected across the hot carrier diode. However, while this particular circuit is relatively simple, the number of solder connections is such that current losses are greater than if a smaller number of solder connections, such as two, were utilized. Additionally, no provision is made in the Hollway et al patent for ensuring that the dipole antenna is oriented properly with respect to the source of microwave energy. With respect to leakages around microwave oven doors, relatively small amounts of energy must be detected. For instance, the Food and Drug Administration promulgated regulations on Oct. 6, 1971 which indicated that the maximum level of acceptability for radiation emitting from a microwave oven would be five milliwatts of microwave energy per square centimeter measured at five centimeters (two inches) from the oven surface. Therefore, since such small amounts of radiation are involved, it is imperative that the dipole antenna be correctly oriented with respect to the source of the radiation. If this is not the case, a detector might incorrectly indicate that a particular microwave oven is not radiating an unacceptable amount of microwave energy, when this is not the case. Furthermore, the device described in the Hollway et al patent can be tested for operability only by placing it into a beaker of water within the microwave oven. This manner of testing is inherently dangerous, by subjecting the user to radiation, possibly damaging or burning the cornea of the eye.
Other patents such as U.S. Pat. Nos. 3,173,091 issued to Strull; 3,828,251 issued to Webb; and 3,927,375 issued to Lanoe et al describe microwave detector devices which suffer from some of the disadvantages described with respect to the Hollway et al patent.